1994 Ford F-150 Engine Idle

It could be an air charge temp sensor or coolant temp sensor too. I do have a couple of questions to ask to be of better help. When was the fuel finlter changed last? Has there been a tune up any time recent? The more info you can give me the better I can help. Get back to me with some info and we will go from there.

Ok so when was a tune up done last and how long ago (mileage) has it been sense the fuel filter was replaced? Do you have a digital multi meter? If you do I have a couple of test for you to do. Get back to me ok.

Ok I would replace the fuel filter so you know that it has been done but I do have some tests for you to run on the TPS and Coolant sensor ok.
TPS first off you need to make sure that it is funtioning right. So back probe the green wire set you meter on 12 volts turn key on engine off. Now with throttle closed you should read around.8 volts now slowly raise throttle it should steadily increase voltage and at wide open throttle it should read arount 4.5 to 5 volts. If there is any stumbles or glitches then it is bad if the voltage it not right then it is bad. Let me know what you find here ok.
Coolant temp sensor- NOw you will need to check ohms at the sensor. So engine off key off unplug the coolant temp sensor it is above the thermostat has a two wire connector on it. You need know what the temp of the engine is roughly ok. So if the engine is a operating temp of about 200 degrees it should be around 2800 ohms.
Let me know what you find here and we will go from there. Now you do not have any vacuum leaks do you? Use a spray bottle with water and while it is idling spray around the intake and the plenum just to make sure there isn't any if there is vacuum leaks it will take in the water and change the idle speed if not kill it. Let see what this brings and go from there.